1. Field of the Invention
The present invention relates to a display LED drive circuit for red color (R), green color(G), and blue color(B) used in an LED unit or the like disposed in large numbers in an LED display device for displaying a video picture, for example, on a large-sized screen.
2. Description of the Related Art
Hitherto, an LED display device having a large number of LED units disposed therein for displaying a video picture on a large-sized screen is known. A display LED drive circuit of the LED unit has a structure, for example, as shown in FIG. 3. The drive circuit shown in FIG. 3 has a red display LED 1r, a green display LED 1g, and a blue display LED 1b connected in parallel for a source circuit 4, and the display LEDs 1r, lg, lb are connected respectively to a constant current circuit 2 or a current limit circuit, which limits an electric current to a constant quantity and to a switching element 3 in series, and then respective switching elements 3r, 3g, 3b corresponding to the respective display LEDs 1r, 1g, 1b are grounded, so that control signals are fed from control signal input terminals 5r, 5g, 5b to the respective switching elements 3r, 3g, 3b to control opening and closing the same, thereby controlling turning ON and OFF of the display LEDs 1r, lg, lb as a load.
Patent Documents 1 to 3 disclose technologies relating to a display LED drive circuit used in a LED display device or the like. Patent Document 1 (JP-T-2001-514432) discloses a structure in which a DC power source is connected to a set of red, green and blue LEDs, and a value of resistance for programming a maximum current which passes through the respective LED set is set, whereby the maximum current passing through the respective LED set is maintained at a constant value in FIG. 1 and so on.
Patent Document 2 (JP-A-2002-244619) discloses a drive circuit including a common driver connected to red, green, and blue LEDs, first switching means for switching supply of voltage from a source circuit in sequence to LEDs of the respective luminescent colors, and second switching means for switching supply of display data for the respective luminescent colors in sequence to the driver synchronously with a switching operation of the first switching means, or a drive circuit including adjusting means for adjusting the voltage to be supplied to the LEDs of the respective luminescent colors according to the voltage drop characteristics of the LEDs for the respective luminescent colors, in FIG. 1 and FIG. 3, and so on.
Patent Document 3 (JP-A-11-191494) discloses a drive control circuit mounted to a band-shaped base member on which a plurality of LED lamp groups are arranged at low density at regular intervals for controlling the light emission of the respective LED lamp groups independently, wherein a shift register that receives input synchronously with a shift clock and stores preset light-emission control data, a latch circuit for reading and storing the light-emission control data according to latch signals, and a drive circuit for illuminating the LED according to the light-emission control data in the latch circuit according to enable signals are integrated therein in FIG. 3 and so on.